Topic

SO₂ acts as a reducing agent when passed through an aqueous solution containing Fe(III) salt. It reduces Fe(III) to Fe(II) i.e., ferric ions to ferrous ions.
2Fe ³⁺ + SO₂ + 2 H₂ → 2 Fe²⁺ + SO₄ ^2- + 4 H⁺

Uses of ClO₂ :
(i) It is used for purifying water.
(ii) It is used as a bleaching agent.

(i) XeO3 can be prepared in two ways as shown.
6XeF₄ + 12 H₂O → 4Xe + 2XeO₃ + 24HF + 3O₂
XeF₆ + 3H₂O → XeO₃ + 6HF
(ii) XeOF4 can be prepared using XeF6.
XeF₆ + H₂O → XeOF₄ + 2HF

(i) XeO3 can be prepared in two ways as shown.
6XeF₄ + 12 H₂O → 4Xe + 2XeO₃ + 24HF + 3O₂
XeF₆ + 3H₂O → XeO₃ + 6HF
(ii) XeOF4 can be prepared using XeF6.
XeF₆ + H₂O → XeOF₄ + 2HF

Anomalous behaviour of fluorine
(i) It forms only one oxoacid as compared to other halogens that form a number of oxoacids.
(ii) Ionisation enthalpy, electronegativity, and electrode potential of fluorine are much higher than expected.

Sea water contains chlorides, bromides, and iodides of Na, K, Mg, and Ca. However, it primarily contains NaCl. The deposits of dried up sea beds contain sodium chloride and carnallite, KCl.MgCl₂.6H₂O. Marine life also contains iodine in their systems. For example, sea weeds contain upto 0.5% iodine as sodium iodide. Thus, sea is the greatest source of halogens.

When chlorine reacts with water, it produces nascent oxygen. This nascent oxygen then combines with the coloured substances present in the organic matter to oxide them into colourless substances.
Cl₂ + H₂O → 2HCl + [O]
Coloured substances + [O] → Oxidized colourless substance

Two poisonous gases that can be prepared from chlorine gas are
(i) Phosgene (COCl₂)
(ii) Mustard gas (ClCH₂CH₂SCH₂CH₂Cl)

ICl is more reactive than I₂ because I?Cl bond in ICl is weaker than I?I bond in I₂.

Air contains a large amount of nitrogen and the solubility of gases in liquids increases with increase in pressure. When sea divers dive deep into the sea, large amount of nitrogen dissolves in their blood. When they come back to the surface, solubility of nitrogen decreases and it separates from the blood and forms small air bubbles. This leads to a dangerous medical condition called bends. Therefore, air in oxygen cylinders used for diving is diluted with helium gas. This is done as He is sparingly less soluble in blood.

It is difficult to study the chemistry of radon because it is a radioactive substance having a half-life of only 3.82 days. Also, compounds of radon such as RnF₂ have not been isolated. They have only been identified.

Nitrogen is chemically less reactive. This is because of the high stability of its molecule, N₂. In N₂, the two nitrogen atoms form a triple bond. This triple bond has very high bond strength, which is very difficult to break. It is because of nitrogen small size that it is able to form pπ?pπ bonds with itself. This property is not exhibited by atoms such as phosphorus. Thus, phosphorus is more reactive than nitrogen.

General trends in chemical properties of group – 15
(i) Reactivity towards hydrogen: The elements of group 15 react with hydrogen to form hydrides of type EH₃, where E = N, P, As, Sb, or Bi. The stability of hydrides decreases on moving down from NH₃ to BiH₃.
(ii) Reactivity towards oxygen: The elements of group 15 form two types of oxides: E₂O₃ and E₂O₅, where E = N, P, As, Sb, or Bi. The oxide with the element in the higher oxidation state is more acidic than the other. However, the acidic character decreases on moving down a group.
(iii) Reactivity towards halogens: The group 15 elements react with halogens to form two series of salts: EX₃ and EX₅. However, nitrogen does not form NX₅ as it lacks the d-orbital. All trihalides (except NX₃) are stable.
(iv) Reactivity towards metals: The group 15 elements react with metals to form binary compounds in which metals exhibit ?3 oxidation states.

Nitrogen is highly electronegative as compared to phosphorus. This causes a greater attraction of electrons towards nitrogen in NH₃ than towards phosphorus in PH₃. Hence, the extent of hydrogen bonding in PH₃ is very less as compared to NH₃.

An aqueous solution of ammonium chloride is treated with sodium nitrite.
NH₄Cl + NaNO₂ ? N₂ + 2H₂O + NaCl
NO and HNO₃ are produced in small amounts. These are impurities that can be removed on passing nitrogen gas through aqueous sulphuric acid, containing potassium dichromate.